Ackman urges General Growth Properties to sell

Shares of General Growth Properties (GGP) spiked as much as 12% Thursday after activist hedge fund investor Bill Ackman urged the shopping mall owner to put itself up for sale.

The company has already been in play, but Ackman, who runs the hedge fund Pershing Square, doesn't want General Growth shareholder Brookfield Asset Management to be the only buyer.

Rival mall operator Simon Property Group (SPG) has unsuccessfully tried to buy General Growth twice over the past two years. During its most recent attempt in October 2011, Simon was roadblocked by Brookfield, noted Ackman in a letter filed with the Securities and Exchange Commission Thursday.

Brookfield then proposed a counter offer to Simon, which included selling 68 General Growth shopping malls to Simon. But Simon wasn't interested and Brookfield has struggled to secure financing for its own purchase, according to Ackman's letter.

In his letter, Ackman accused Brookfield of obstructing Simon's acquisition by causing the REIT to be "effectively handcuffed and gagged from considering or proposing a transaction for which it needs no financing." Ackman owns roughly 10.2% of General Growth.

As an activist shareholder, Ackman typically urges company to break themselves up or sell, but recently he's also pushed companies to make operational changes. At JCPenney (JCP), where he owns a large stake, he pushed the board to hire new CEO Ron Johnson, Apple's (AAPL) former retail chief.

He also recently disclosed a stake in Procter & Gamble (PG) but his plans there are so far unclear.

Maureen Farrell is a staff writer at CNNMoney and covers Wall Street, banking, mergers and the stock and bond markets. Prior to joining CNNMoney, she covered venture capital and entrepreneurs for Forbes, and mergers and bankruptcy for Mergermarket and Debtwire, both divisions of the Financial Times.